2010-07-13

Opportunity Sol 522 (Spirit Sol 543)

Surprisingly, visodom performed well through the entire drive yestersol. We'd been worried visodom wouldn't work reliably with nothing but our own tracks for it to look at, but so far, so good.

The drive itself went where it was supposed to. We're at the end of one trough, and thisol our plan is to hop into the next one (about 5m worth of driving, in a lazy "S") and drive about 10m along it, to a point where the terrain seems to fall off slightly. If we could see it better in the NCAM coverage, we might be able to drive farther -- or so I think. Later the PCAMs arrive, and they show that, yep, the terrain appears to fall off a bit there. Oh, well; we're using up all the time we've got anyway. (Visodom works, but it's slow! This 15m of driving will take us about 2.5 hours. We'll actually spend maybe 10 minutes turning the wheels; all the rest of that is visodom overhead.)

It's Rob Sullivan's first sol as SOWG chair. He does a great job, but at one point, when he's having trouble reaching consensus on what science should be slotted into the tiny amount of time left over after driving, he passes on a bit of wisdom: "One of the things Steve told me was that you've failed as SOWG chair if you have to decide rather than reach consensus." They reach consensus.

We're settling on a drive template, which makes things easier. Between the enormous setup block and the smaller teardown block, we cut the drive into a series of segments each about 5m long. Between segments, we reseed visodom -- slow, but necessary to work around a flight software bug that causes visodom's estimated roll and pitch errors to accumulate, which can abort the drive. And at the start of each segment, we zero the failure count and choose a new max failure count for that segment. This helps us play by the Rules of the Road, which demand that we catch slip -- if we've bogged down entirely, visodom will fail to converge and the error limit will stop us. (We can't just choose a single count large enough for the entire drive, because then we can dig in a lot more before stopping. The approach we've come up with uses several smaller counts instead, making the trigger more reliable.)

I also remember something we forgot on yestersol's drive: at the end of the drive, we have to straighten the wheels. The end of yestersol's drive included a last-minute comm turn, which left the wheels cocked in. There's nothing inherently wrong with this, but if another steering actuator should fail on this vehicle, we want it to "fail straight," since that's the least bad configuration for continued driving. I've made quite a point of this in my "Driving a Mars Rover for Dummies" talk -- which I've given twice publicly now -- so I'd feel like twice as much of a dumbass if I forgot this on some sol when it really mattered!